1. Field of the Invention
The present invention relates to the manufacture of laminated glass assemblies.
2. Discussion of the Background
Laminated glass assemblies formed by (1) a monolithic or laminated glass and/or plastic support in combination with (2) a sheet of plastic comprising at least one polyurethane layer can be used advantageously as front windshields or rear windshields for motor vehicles, or even as windows for buildings. The mounting of these glass assemblies in the bay of an automobile body which has traditionally been done using a profiled joint in a resilient material is more and more frequently being replaced by mounting by gluing the glass directly onto the body.
In effect, this type of mounting has advantages. In particular, it holds the windshield in the bay of the body in case of a violent shock. It can easily be automated and, in addition, it provides a flush mount of the glass to the body which reduces the air drag coefficient of the vehicle.
When a conventional laminated glass assembly, that is, a glass formed by two sheets of glass and an interposed sheet of an energy-absorbing material such as polyvinylbutyral, is mounted, the gluing of the glass onto a fold in the sheet metal of the body is carried out by the deposit of an appropriate adhesive cord onto a glazed edge arranged on the periphery of the surface directed towards the passenger compartment. This is intended to protect the adhesive from UV radiation and also to hide the unesthetic glue joint from view.
In the case of safety glasses to which the present invention relates and which are formed by a rigid support and a sheet of flexible plastic, the glazed edge is provided on the surface of the support which is directed towards the passenger area, that is, the one in contact with the plastic sheet and, in particular, in contact with the polyurethane layer. For this type of safety glass, the glazed edge is a source of manufacturing difficulties for the glasses. In particular it creates a problem of adhesion of the plastic sheet onto said glazed edge. The problem can be insufficient gluing at the moment of manufacture of the glass itself or during the preliminary calendering assembly operation when this operation is used for assembly. In certain cases instantaneous detachment of the plastic sheet at the location of the glazed border can be observed. This detachment is a serious problem which cannot be repaired during the final assembly operation using an autoclave cycle, for example.
Even where there is no immediate detachment, the bond is still generally not sufficiently strong or it even becomes damaged when the glass is subjected to more rigorous climate conditions than those generally encountered in a shop for manufacturing laminated glasses. For example, problems can arise when the glass is placed in a very damp atmosphere.
When the plastic sheet does not have to act as an energy absorber it is possible to solve the adhesion problem by using a plastic sheet cut to a more reduced format such that it does not cover the glazed band. The gluing of the glass then is carried out as in the case of conventional laminated glasses by the deposit of the glue joint directly onto the glazed band.
However, when the plastic sheet must act as an energy absorber and it has the qualities required for that purpose, it is necessary to directly glue the periphery of the sheet onto the bay of the body with satisfactory adhesion. This level of adhesion between the sheet and the support must be maintained over time. This is essential to confer its safety properties to the glass.
Thus existing technology suffers from problems of poor adhesion between the plastic sheet in the support. There is accordingly a strongly felt need for a solution to this problem.